It is generally known that, in conjunction with exhaust emission control systems for reducing nitrogen oxide emissions, so-called selective catalytic reduction (SCR) is used in which NOx conversion in a lean atmosphere is achieved by means of specially tuned catalytic converters. To reduce NOx, a suitable reducing agent is introduced into the exhaust gas flow in order to obtain final products such as N2, CO2 and H2O. For example, ammonia or urea is used as the reducing agent in concert with active SCR catalytic converters. For mixing of the reducing agent with the exhaust gas, a static mixer is conventionally used, by means of which the desired distribution of the reducing agent in the exhaust gas flow for efficient exhaust emission control is to be achieved.
U.S. Pat. No. 5,489,153 already discloses a generic static mixer for a flow channel which has a plurality of so-called deflection elements in the flow channel. The deflection elements here are arranged in rows on a rectangular supporting grid. By means of this static mixer, the incoming flow is to be deflected by the deflection elements in different directions, the deflection elements generating a transverse flow—relative to the primary direction of flow—in the individual openings of the supporting grid. Especially effective mixing is thereby to be achieved by the production of swirls, in particular by the formation of rotating vortices. But the problem in conjunction with a static mixer of this type having a rectangular grid structure is that cracks and failures in the supporting grid region of the mixer can occur at very high exhaust gas temperatures and/or during temperature changes with large gradients.
Therefore, the object of this invention is to provide a static mixer for an exhaust gas system of an internal combustion engine-driven vehicle, in particular a motor vehicle, by means of which the risk of mixer damage is to be reduced in a structurally simple and operationally reliable manner.